Steering Surface Reactions of ZnIn2S4 Unlocks Photocatalytic Z-Scheme Overall Water Splitting

Abstract

Narrow-band-gap metal sulfides are effective for sacrificial hydrogen production; however, their application in photocatalytic Z-scheme overall water splitting (OWS) is hampered because of severe competing reduction reactions, sluggish oxidation conversion of redox couples, and photocorrosion. To address those challenges, ZnIn2S4 is employed as a prototype for [Fe(CN)6]3−/4−-mediated Z-scheme OWS in this work, over which a series of tailored surface modifications has been designed and successively implemented. The detailed results show that Cr2O3 layer modification over the Pt reduction cocatalyst can effectively suppress the reverse and side reactions, IrO2 oxidation cocatalyst modification can accelerate the [Fe(CN)6]4− oxidation kinetics, and the thin TiO2 coating layer passivates ZnIn2S4 against photocorrosion. Synergizing these surface modification strategies enables the construction of a stable visible-light-driven Z-scheme OWS system, integrating the surface-engineered ZnIn2S4 photocatalyst as a hydrogen evolution photocatalyst, and [Fe(CN)6]3−/4− and Au/FeCoOx-BiVO4:Mo as a redox mediator and oxygen evolution photocatalyst, respectively. To further promote such an assembled photocatalyst system, the Pt single atom cocatalyst with uniform dispersion on ZnIn2S4 is realized by a developed adsorption-photoreduction approach, markedly accelerating charge separation and transfer. Consequently, the optimized reaction reaches an apparent quantum yield of 1.5% at 420 nm, making it among the highly efficient reported metal sulfide-based Z-scheme OWS systems. This work unravels key bottlenecks limiting metal sulfides in effective Z-scheme OWS and provides a paradigm of tailored surface modifications to solve those issues toward efficient artificial photosynthesis.